The invention relates to a push-in coupling for pipes comprising a sleeve and a holding device which contains a clamping ring for joining a pipe end to the sleeve.
European patent application No. EP 587,131 discloses a push-in coupling of this kind, which has a coupling sleeve, a holding means in the form of a clamping device, and an operating device. The coupling sleeve is configured as a dual sleeve, so that with this push-in coupling the ends of two plastic pipes can be joined together with the two clamping devices. The holding means contains a clamping ring which has externally a clamping taper and internally at least one clamping rib which can be brought into engagement with the pipe end. By means of a sleeve nut which can be threaded onto the coupling sleeve the opposite taper can be gripped by the clamping ring. Also, a sealing ring is disposed in the coupling sleeve. When applying the coupling care must be taken that the pipe end is inserted far enough into the coupling sleeve so that the clamping ring and likewise the sealing ring can perform their functions. There is a danger, however, that as a result of incomplete insertion of the pipe end into the push-in coupling, the connection will fail to hold or will be defective.
Published German Patent Application No. DE 3,112,255 discloses a quick coupling for pipes having a holding system which comprises an axially displaceable hold-back means. The hold-back means contains axial slits and is disposed partially within a rigid ring with a circular rib. The hold-back element consists of resilient-elastic material and has a rib directed radially outward, as well as a conical surface at the front end, which corresponds with a taper of an intermediate element. When a pipe is inserted, first the hold-back means and the surrounding ring with the circular rib are moved in the axial direction until the ring comes into contact with a bottom of the sleeve body. As insertion of the pipe continues, the radial ring of the hold-back means moves past the circular rib, while the resistance to insertion increases and the hold-back means is pressed radially against the outside surface of the pipe. If the rib of the hold-back means is all the way past the circular rib of the ring, the rib enters into an annular groove in the ring, while the given resistance to the insertion movement suddenly ceases. Thereupon the pipe together with the hold-back means and the snapped-in ring is moved forward contrary to the insertion movement until the conical surface of the hold-back means is tightened against the cone of the intermediate element. The specification and the adjustment of the force of resistance requires a not inconsiderable production difficulty involving close tolerances, especially in the hold-back means and of the ring with the circular rib. Close limits must also be observed for the outside diameter of the pipes, since otherwise the teeth of the hold-back means are forced only partially into the pipe and the pipe can be pulled back out of the coupling. The prior-art coupling furthermore permits relative axial movements of the pipe with respect to the coupling, and foreign bodies can come within the reach of a gasket placed between a nut and the intermediate element and there is a danger of leakage of the medium under pressure from the pipe.
Furthermore, German Utility Model No. DE-U 93 08 181 discloses a connection fitting for pipes which has a connecting means that can be fastened to a pipe end and an annular groove for a sealing ring. A pilot ring which can be moved by the pipe end past the sealing ring during assembly is present, which has a surface for contact by an end surface of the pipe end. When the pipe end is inserted, the pilot ring has to be pushed by the sealing ring, with the need to overcome increased resistance to insertion. When the pilot ring has been pushed completely through the sealing ring, the resistance decreases markedly. Damage to the sealing ring by the pipe end is said to be prevented by the pilot ring without the need to chamfer the pipe end.
A push-in coupling for pipes, hoses or similar round bodies also is disclosed in Published German Patent Application No. DE 4,304,241, which comprises a holding means and at least one sealing ring in a receiving sleeve. The holding means contains, radially within it, a slotted or fan-like holding disk whose tongues sloping radially inward toward the sleeve bottom serve for clamping the exterior surface of the inserted pipe end. In this push-in coupling also the danger is that the pipe end will not be inserted far enough and the required connection will not be properly established.